1. Field of the Invention
The present invention relates to a semiconductor light projection apparatus which comprises an optical system for projecting lights emitted from a plurality of semiconductor light emitting devices onto a light projected area, and a distance measurement apparatus which comprises the semiconductor light projection apparatus and receives reflected light from an object to detect a distance from the object.
2. Description of the Related Art
A distance measurement apparatus has been developed, which projects light to a detected area from a semiconductor light projection apparatus built therein, constituted by semiconductor light emitting devices such as a semiconductor laser device and a light emitting diode, and receives the reflected light to measure a distance from a measured object in the detected area based on a delay time.
The distance measurement apparatus is used for a system which measures a distance between a certain automobile loading this apparatus and another automobile and gives an alarm when the distance between the automobiles becomes smaller than a predetermined value, and for a system which measures a distance from the certain automobile to another automobile or an obstacle during parking and gives the alarm when the distance therebetween is smaller than a predetermined value. The distance measurement apparatus is used also for a system which gives the alarm when light is intercepted at a range within a predetermined distance in a light projected area.
Furthermore, a system is devised, which controls a running of the automobile and facilitates the safe and proper running of the automobile by utilizing these systems.
In this case, considering also running conditions on a superhighway, the inter-automobile distance measurement system is required to be capable of measuring the distance between the automobile and another automobile running in front, which ranges from about 10 m to about 100 m or more, for example, about 120 m. To cope with this requirement, the semiconductor laser devices must be driven so as to perform laser oscillation at pulses of several tens to several hundreds nsec and emit light exhibiting power of about 20 W to about 80 W in total. In general, one semiconductor laser device can emit light exhibiting power of about 10 W to about 20 W when a peak current is set to about 20A. Accordingly, in order to meet above described requirement, it is conceived that one semiconductor laser device is driven with a large current or alternatively a plurality of semiconductor laser devices are simultaneously driven and light outputs from them are synthesized.
Since a life time of the semiconductor laser device lowers in reverse proportion to a magnitude of current, to drive one semiconductor laser device with a large current is not said to be a good condition for the device. Accordingly, a method which allow a plurality of semiconductor laser devices to perform laser oscillations and collect lights emitted from them to achieve a large amount of lights will be available.
As this method, a method which allows the semiconductor laser devices to emit lights by driving the semiconductor laser devices individually, each being coupled in parallel to a light source, and collects these lights is conceived. However, when this method is adopted, driving currents of the number equal to that of the semiconductor laser devices coupled in parallel to the light source must be made to flow therethrough, so that a quantity of power consumption becomes large and sharpness of waveforms of pulses is lost. Accordingly, this method is not very desirable in terms of driving conditions.
On the other hand, to solve such drawbacks, there have been methods, which are disclosed in Japanese Patent Applications Laid-Open Nos. 5-41561, 6-282807 and 7-307520. In these methods, a plurality of semiconductor laser devices are laminated so as to be integrated with each other and they are driven in the state where they are in series coupled to each other, and a plurality of light emission points as a light source are arranged at intervals of about 100 xcexcm. The lights from the light emission points are collected by a collection lens and converted to a parallel light, and the parallel light is projected onto a projected area.
In this case, even when the interval between the light emission points in the light source is 100 xcexcm, intervals between spots of laser beams from the semiconductor laser devices spread in proportion to a projection distance. As shown in FIG. 25, for example, a semiconductor laser apparatus 1 constituted by stacking three semiconductor laser devices 1a to 1c is disposed at a focal position of a collection lens 2 as an optical system, and the semiconductor laser apparatus 1 is allowed to emit light. Laser beams emitted from light emitting points La to Lc of the corresponding laser devices 1a to 1c are collected after passing through the collection lens 2, and converted to parallel lights Sa to Sc.
At this time, when a diameter of each spot of the parallel lights Sa to Sc is D, a shift equal to that the interval of the arrangement of the laser devices 1a to 1c is created at a position distant from the devices 1a to 1c by a focal length f. Since a spot diameter becomes large to some degree practically, such shift is not a problem, and a state that the lights are collected is kept. When such parallel lights Sa to Sc travel by a distance to be objected, for example, by about several ten meters, the above described shift is widened to a degree that cannot be neglected. Thus, effects that the detection distance is lengthened is entirely lost by collecting the lights.
This state is illustrated in FIG. 26. Specifically, if it is intended to lengthen the detection distance X, lights are projected so as to overlap spots when the detection distance is about X1. When the detection distance is lengthened to about X2 larger than X1, not only a reduction of a quantity of light is brought about, but also formation of a dark area B where light is not projected is created by enlarging a distance between the spots. In this case, a measured object positioned in the dark area B accidentally in measuring the distance is not measured, so that the measured object is recognized as that no object exists. A disadvantage that a precise measurement can not be performed is brought about.
A degree of the spread of the interval between the spots is in proportion to a distance from the collection lens 2, and as the distance from the collection lens 2 becomes larger, the spread of the interval between the spots becomes larger simply. Thus, a reduction of a quantity of light and occurrence of the dark area becomes remarkable, and this is a disadvantageous condition when it is intended to receive much reflection light from the object.
The reduction of a quantity of the reflection light is estimated in the following manner. When the distance between the light emission points La to Lc is assumed to be 100 xcexcm, a spread angle xcex8 of the light source with respect to the focal length f of the collection lens 2 is expressed by the following formula.
xcex8=arctan (0.1/f)
If the focal length f is 22 mm, the spread angle xcex8 becomes 0.26xc2x0. In a position apart from the position of the collection lens 2 by 22 mm that is 1000 times as long as the focal length f, a distance between centers of the spots is about 10 cm. Since the position of the center of the spot is sure to be shifted even when the spot diameter D is considered, a quantity of light per unit area reduces owing to the spread of light in the projected area. Accordingly, a quantity of light is surely reduced.
Therefore, when it is intended to set a distance of 100 m or more as a range of a measured distance, a quantity of light significantly and also a dark area occurs. It is necessary to take a countermeasure to increase the quantity of light by driving the semiconductor laser with large current. In this case, lowering of a life time of the semiconductor laser cannot be prevented.
Furthermore, a constitution in which a range of the measured distance is set to a remote distance of 100 mm or more is obtained, a strong light is emitted. When such strong light is to be emitted, an emission level of the light must be set under consideration of safety in using the apparatus in circumstances where such strong light is incident onto eyes of human being. Also in this point, a technological subject for a high emission of light is left.
The present invention was made in view of the above described circumstances, the object of the present invention is to provide a light projection apparatus which is constituted by using a plurality of semiconductor light emitting devices, which is capable of emitting light of a high intensity with small current, and performing an effective projection operation in accordance with a projection distance, and to provide a distance measurement apparatus which is capable of effectively performing a distance measurement using the semiconductor light projection apparatus.
Another object of the present invention is to provide a semiconductor light projection apparatus which is capable of securing safety for eyes of human being in using the apparatus under circumstance where strong light may be incident onto the eyes when the apparatus must project the strong light onto a remote position to achieve the foregoing object, and to provide a distance measurement apparatus which measures a measurement distance using the semiconductor light projection apparatus.
According to one aspect of the present invention, since a plurality of optical devices are disposed for corresponding semiconductor light emitting devices so as to project light onto a light projected area and the plurality of light emitting devices are in series connected to a power source so as to be supplied with a power, current equal to that to be supplied to one semiconductor light emitting device is supplied to all of the light emitting devices, so as to allow the light emitting devices to perform light emitting operations. Thus, a quantity of light equal to that emitted by all of the semiconductor light emitting devices connected in series can be obtained.
Specifically, in the semiconductor light emitting device, light emitting phenomenon occurs by allowing current to flow therethrough in a certain direction. Accordingly, when the semiconductor light emitting devices are in series connected to each other, all of the semiconductor light emitting devices emit lights. At this time, as in the first aspect of the present invention, a light emitting diode device, a semiconductor laser device, an electroluminescence device (EL device) and the like do exert almost no resistance, so that all of devices connected in series emit lights. Thus, an intensity of light emission equal to that emitted by the devices of the number can be obtained by supply of current equal to be supplied to one device.
Since the light obtained from each semiconductor light emitting device can be projected to the light projected area by the individual optical device, by collecting the lights emitted from the semiconductor light emitting devices without separating them the collected lights with a high intensity can be projected onto one spot. Alternatively, it is possible to perform the projection operation for the corresponding light projected areas, individually.
According to another aspect of the present invention, in the semiconductor light projection apparatus adopting the above described constitution, with reference to a package accommodating a semiconductor device of the semiconductor light emitting device by loading it thereon, the semiconductor device is fixed to the package by fixing a metallic pedestal onto a metallic base, using a metallic base and an ordinarily case having three terminals including a terminal electrically conducting to the metallic base. The semiconductor device can be accommodated within the package without using another package exclusively used. In this case, by bonding other two terminals formed so as to be insulated from the metallic base and both electrodes of the semiconductor device to each other, a constitution drawing out the terminals suitable for connecting the light emitting device in series can be obtained.
The terminal electrically conducting to the metallic base can be kept at a predetermined potential which has no relation with an operation of the semiconductor device. In other words, the terminal is connected to, for example, the ground terminal, a potential of the whole of the package is kept a stable state, and the semiconductor devices of the semiconductor light emitting devices can be made to be a state where they are connected in series to each other. Moreover, even when a heat radiation fin is fitted to the whole of the package, an electrical insulation from the semiconductor device is established. Handling for heat radiation is made to be easy, and a stable operation can be achieved.
According to another aspect of the present invention, in the above described package, the metallic pedestal is provided so as to be insulated from the metallic base, and the semiconductor device is loaded onto the metallic pedestal so that its rear surface electrode is made to be electrically conduct to the metallic pedestal, and fixed to the metallic pedestal. Moreover, the surface electrode and the metallic pedestal are connected to the two terminals which do not electrically conduct to the metallic base by bonding wires. Thus, the semiconductor device can be provided so as to electrically conduct to the metallic pedestal, and an electric connection with the rear surface electrode of the semiconductor device can be achieved interposing the metallic pedestal, so that assemble operations can be simplified.
According to still another aspect of the present invention, in the package constituted as above, the semiconductor device is loaded on the metallic pedestal in a state where a conductor pattern electrically conducting to the rear surface electrode is interposed between the semiconductor and the metallic pedestal as well as in the semiconductor device is electrically insulated from the metallic pedestal, and fixed to the metallic pedestal. The surface electrode and the conductor pattern are connected to the two terminals which do not electrically conduct to the metallic base by bonding wires. The rear surface of the semiconductor device and the metallic base are made to be in an insulated state, without depending on whether or not an insulation state between the metallic base and the metallic pedestal is created. In addition, an electrical connection with the rear surface of the semiconductor device interposing the conductor pattern therebetween can be achieved. Limitations in fixing the metallic pedestal to the metallic base are lessened, thus simplifying the steps.
According to still further aspect of the present invention, in the above described constitution, since the semiconductor device is loaded interposing an insulating plate on a surface of which a conductor pattern is formed and fixed thereto, another conductor pattern needs not to be provided newly, thus simplifying the constitution and reducing the number of assembly steps.
According to still another aspect of the present invention, in a semiconductor light projection apparatus adopting a semiconductor light emitting device that is a current-driven type two terminal device, the package which loads the semiconductor device to accommodate it is a package exclusively used for a certain purpose, which is constituted by a metallic base, a metallic pedestal fixed to the metallic base in a state insulated from the metallic base, and two terminals, so that a fabrication is simplified. Although a terminal electrically conducted to the metallic base is not provided, when a contact with a potential of a portion fixing the package is made, the ground potential is, so that a stability is established, and it is possible to prevent to give an adverse effect to the semiconductor device.
According to still another aspect of the present invention, in the semiconductor light projection apparatus adopting a semiconductor light emitting device that is a current-driven type two terminal device, the semiconductor device is formed to a mesa shape, and an electrode is formed on its step difference portion and a surface portion, whereby an electrode structure in which a current supply from the same surface side is performed is obtained. The package is constituted by a case including a metallic base and three terminal including a terminal electrically conducting to the metallic base, and a metallic pedestal for bonding the semiconductor device, the metallic pedestal being fixed onto the metallic base. The semiconductor device is constructed such that the electrodes on the step difference portion and the surface portion and the two terminals which do not electrically conduct to the metallic base are connected by bonding wires, respectively. Any of the bonding wires is connected to the front surface of the semiconductor device without depending on the electrode of the package and the terminal structure, thus simplifying the fabrication steps.
According to still another aspect of the present invention, in the semiconductor light projection apparatus adopting a semiconductor light emitting device that is a current-driven type two terminal device, the package constituting the semiconductor light emitting device providing a plurality of semiconductor devices therein so as to be integrated with each other is constituted by at least two terminals provided so as to correspond to both terminals when metallic pedestals for device bonding and the plurality of semiconductor devices are in series connected, the metallic pedestals corresponding to the number of the metallic bases and the semiconductor devices. The plurality of semiconductor devices are in series connected by bonding wires in a state where the plurality of semiconductor devices are bonded on the metallic pedestals so as to be fixed thereto. Thus, the plurality of semiconductor devices can be provided in one package integrally therewith in a state where they are in series connected to each other. The apparatus is compacted, and handing of it is simplified. Moreover, since the semiconductor devices are bonded at approximately certain points, adjustment for the optical system is comparatively simplified.
According to still another aspect of the present invention, in the above described constitution, since a cover formed integrally with a lens as an optical system corresponding to a light projections of each of a plurality of semiconductor light emitting devices is provided, handing is more simplified. By previously performing an adjustment of the lens, the adjustment of the optical system needs not to be further performed, thus achieving a significant reduction of the number of the fabrication steps.
According to still further another aspect of the present invention, in the semiconductor light projection apparatus using the package in the above described constitutions, since at least two bonding wires are provided for each connection portion of the semiconductor device, the semiconductor light projection apparatus can be used without reducing a reliability of an operation in spite of the constitution in which the plurality of semiconductor light emitting devices are in series connected. For example, in the case of malfunction due to breaking of any of t he bonding wires, an electrical conduction can be kept through remaining bonding wires. As troubles expected to occur in the semiconductor light emitting device, short-circuiting trouble occurs generally. In this case, since current supplies to other semiconductor light emitting devices can be kept, it is possible to keep the light projection state as a whole.
According to still another aspect of the present invention, in the above described semiconductor light emitting apparatuses, since a semiconductor laser device is used as the semiconductor device, a light projection operation with a higher efficiency can be performed by performing spotting for light by an optical system as a light source, so that the light projection which projects light with a high density to a remote distance can be performed. Laser beams from the semiconductor laser devices can be collected, thus further increasing its efficiency.
According to still another aspect of the present invention, since the semiconductor device emitting light a wavelength of which is set to 1.4 xcexcm or more is used, the wavelength of the light i s included within an eye safe region of a safety standard MPE (Maximum Permissible Exposure) defined in JIS (C6802) in case of performing pulse lighting. Even when strong light is irradiated onto a remote position under circumstances where the light may be incident onto eyes of human beings, the light can be projected safely without giving bad influence to the human body. In other words, it is possible to emit light with a high power without any limitation to an output which is limited in the wavelength of 1.4 xcexcm or less.
According to still further another aspect of the present invention, in the above described semiconductor light projection apparatuses, since a plurality of optical devices are constituted to a state where optical axes thereof are adjusted so as to collect lights emitted from the plurality of semiconductor light emitting devices to project collected light onto one projected area, the light projection can be performed with a high light density even when the light is projected to a remote distance, and since the lights individually diaphragmed by the optical systems are collected, an effective light projection operation can be performed by providing a light collection point at a position in accordance with a projection distance.
According to still further another aspect of the present invention, in a semiconductor light projection apparatus in which optical axes of optical devices are adjusted so as to project collected light onto one light projected area, each of lights being emitted from corresponding one of a plurality of semiconductor light emitting devices, when spots in the light projected area projected by the semiconductor light emitting devices take an ellipsoidal shape, a plurality of optical devices are disposed so that each optical axis of the optical devices is parallel with others on the same plane and at equal intervals, and a plurality of semiconductor light emitting devices are disposed so that spots at the light projected area overlap others by creating a shift in a major axis direction of the ellipsoidal shape. Overlapping portions of the spots in the major axis direction at the light projected area, which are produced by irradiation of the semiconductor light emitting devices shift by a quantity equal to an interval of the semiconductor light emitting devices. As a result, an area where the spots overlap when the lights from the semiconductor light emitting devices are irradiated by the optical devices in parallel, that is, an area, which can be used as the strongest light, becomes a larger rate with regard to a shift quantity which becomes larger as the distance to be irradiated becomes larger. In a remote position which needs a strong light, a overlapping degree is increased, thus effectively irradiating the light.
According to still another aspect of the present invention, in the semiconductor light emitting apparatus in the above described aspect, a plurality of optical devices is constructed in a state where optical axes thereof are adjusted so that lights emitted from a plurality of semiconductor light emitting devices are projected onto a plurality of projected areas. Accordingly, a projection operation can be performed using the projected lights by the semiconductor light emitting devices individually. Also in this case, since the semiconductor light emitting devices are in series connected, a power supply operation can be effectively performed.
According to still another aspect of the present invention, the lights emitted from the plurality of semiconductor light emitting devices are collected, and the collected lights are projected onto a light projected area using semiconductor light projecting apparatuses in which optical axes thereof are adjusted so as to project the collected lights onto one light projected area. At this time, by detection means a time from a light projection time of reflection light to a light receiving time is measured, thus detecting a distance to an object. Accordingly, as described above, lights to be projected are collected effectively, and can be projected onto a light projected area, thus enabling a distance measurement to a more remote distance precisely within the light projected area. In other words, it is possible to perform an effective light projection operation within a distance measurement range to be objected.
According to still another aspect of the present invention, in the above described distance measurement apparatus, since by detection means the semiconductor light emitting devices of the semiconductor light emitting apparatus are allowed to perform light emission in the form of pulses, a light projection operation with a high power can be performed effectively, and a time difference between the light emitted in the form of pulses and a reflection light received by light receiving means is detected based on a difference between rising times of a light projection signal and a light receiving signal, so that a distance can be measured and a measurement with a high reliability can be performed with iteration of the measurement.
According to still further another aspect of the present invention, in the above described distance measurement apparatus, optical axes of the optical devices are adjusted so that a light collection point of lights emitted from the plurality of semiconductor light emitting devices are disposed within a range of a detection distance. A shift of a center point of light emitted from each semiconductor light emitting device can be lessened within the range of the detection distance, and a reduction in a quantity of light can be prevented as possible, thus performing a precise detection operation.
According to still another aspect of the present invention, in the above described distance measurement apparatus, since a position of the light collection point is adjusted to the remotest point within a range of a detection distance, a collection degree of lights from the semiconductor light emitting devices becomes best at the remotest point, thus suppressing occurrence of a shift of a center point. As the light collection point becomes remoter, the collection degree of lights becomes higher. It is possible to suppress a reduction of a quantity of light owing to a shift of a center point. In addition, at a position near than the remotest point, since the semiconductor light emitting devices are disposed in suitable intervals in spite of the shift of the center point of the light is maximum, by appropriately setting a relation between the disposition interval and the spot diameter diaphragmed by the optical system, a collection state in which the shift does not almost exist all over the range of the measurement can be brought about, thus achieving an increase in a detection precision within the range of the distance measurement.
According to still further another aspect of the present invention, in the distance measurement apparatus in which optical axes are adjusted so that a light collection point is positioned within a range of a detection distance, the light collection point being a point where lights emitted from the semiconductor light emitting devices are collected, since a position of the light collection point is adjusted to a middle point within the range of the detection distance, a collection degree of light is highest near the middle point, the shift of the center point is approximately equal to each other in both of the remotest point of the detection range and the nearest point thereof, and this can be set as conditions in which the shift of the center point of the spot light emitted from the semiconductor light emitting devices is least over all of the detection range. Thus, by setting as the light collection point a distance in which a detection precision is highest within the range of the distance measurement, a quantity of light near the light collection point is most increased, thus achieving the detection precision.
According to still further aspect of the present invention, in the above described distance measurement apparatuses, a predetermined range is scanned in a light projection direction by projection light scanning means, and the distance of the object is obtained corresponding to the light projected area based on reflection light detected by detection means. Accordingly, it is possible to detect a range to be projected by dividing it into a projected area, and it is possible to detect a position in which a detected object exists within a wide detection range and a distance in accordance with the projection position. Thus, the detection operation within a wide range can be performed with a higher precision.
According to still further another aspect of the present invention, in the above described constitutions, since the light projection scanning means scans two-dimensionally in the light projection direction, a degree of freedom for setting a range of the detected object is increased, and the range of application use can be also increased.
According to still further aspect of the present invention, the distance measurement which measures a distance by measuring a propagation time of the reflection light is loaded on a moving body, and a distance within a light projected area existing in its running direction is detected. Accordingly, in a moving body used as traffic means such as automobiles or a manned or unmanned moving body such as transportation apparatuses and robots, a distance to an object within a light projected area in a running direction can be detected. As a result, the distance measurement apparatus can be applied to wide applications in such manners that obstacles disturbing advances of men or objects, which exist in a running direction, are detected, or an object to be pursued is detected.
According to still further another aspect of the present invention, the distance measurement apparatus can be used by loading this apparatus on automobiles in the following manners. Specifically, when obstacles existing in a running direction is detected by loading the distance measurement apparatus on automobiles, notification is made by alarming occurrence of dangerous situations, a proper measure such as reducing a speed is taken. When an automobile pursues another automobile running ahead, the automobile running ahead is detected, and running is controlled while keeping a suitable distance between the automobiles.
Furthermore, in the moving body which does not run on tracks, a deviation between the running direction and the direction of the automobile sometimes becomes large. Also in this case, the detection range is scanned and the distance is detected, whereby detected information can be utilized by selecting only a man or an object existing in a position corresponding to the running direction. Moreover, in the case where a semiconductor laser device is used as the semiconductor light emitting device, the detection range can be set to a remote distance. Specifically, a distance of about 100 m or more can be detected surely so as to keep properly a distance between the automobile loading the apparatus and the automobile running ahead on a highway.
According to still further another aspect of the present invention, in a distance measurement apparatus which is loaded on a moving body and detects a distance in a light projected area corresponding to its running direction, in the case where spots in the light projected area of the semiconductor light emitting devices take an ellipsoidal shape, the spot of light emitted by the semiconductor light projection apparatus is set so that a major axis direction of the ellipsoidal shape is arranged in a perpendicular direction to a road surface. Accordingly, a detection resolution in a horizontal direction of a moving plane can be raised. Thus, when this apparatus is used for, example, automobiles, it is possible to detect the direction and position of the body existing in the running direction.
According to still further another aspect of the present invention, a semiconductor light projection, in which an optical axis is adjusted so as to project lights emitted from a plurality of semiconductor light emitting devices onto a plurality of light projected areas, is provided. Reflection lights from an object existing on the plurality of light projected areas of the semiconductor light projection apparatus are received by light receiving means. A distance to the object existing in the light projected areas is detected. Thus, a wide detection area can be set, and the object existing in the detection area can be detected.
According to still further another aspect of the present invention, the above described constitution is loaded on a moving body and an object in the light projected area which is set around the moving body is detected. When an automobile and a unmanned transportation automobile run so as not to touch objects around them, this apparatus can be used. Alternatively, this apparatus can be used for preventing that damages of the automobiles occurs owing to collision with objects around the automobiles in a narrow region.